1. Field of the Invention
The present invention relates to an axial-flow fan, and more particularly, to an axial-flow fan that can reduce the camber ratios of blades up to a range between 33% and 85%, thereby achieving a very low noise level.
2. Background of the Related Art
An axial-flow fan includes a circular central hub and a plurality of blades radially arranged along the circumference of the hub, and as well known those skilled in the art, the axial-flow fan is a kind of fluid machinery and serves to blow air in the axial direction by the rotation of the plurality of the blades. A representative example of the axial-flow fan is a cooling fan that promotes heat radiation of an air-cooled heat exchanger, such as an electric fan, a ventilation fan, and a radiator or condenser of an automobile, by blowing air to or drawing air from the heat exchanger.
The axial-flow fan that is used as the cooling fan of the heat exchanger in the air conditioning system of the automobile is mounted in the rear or front of the heat exchanger in conjunction with a shroud that is provided with a plurality of airflow guide vanes that serve to guide the air blown by the blades of the fan to an axial direction from the front or the rear of the heat exchanger. The axial-flow fan may be classified into a pusher-type axial-flow fan assembly and a puller-type axial-flow fan assembly in accordance with the arranged positions with respect to the heat exchanger.
As shown in FIGS. 1 and 2, the general axial-flow fan 1 of an automobile is mounted in conjunction with a shroud 2 surrounding the blades of the fan and guiding air toward the axial direction, in the front of the heat exchanger. The axial-flow fan 1 includes a central hub 12 connected with the driving shaft of a motor 3, a plurality of blades 11 extending radially outwardly from the hub 12, and a circular fan band 13 to which the peripheral ends of the plurality of blades 11 are fixed for surrounding the plurality of blades 11. The axial-flow fan is generally made of synthetic resin and integrated with the blades 11 into a single body. The plurality of blades 11 that are curved in the plane of the fan 1 are rotated as the motor 3 is rotated, thereby producing a difference pressure of the airflow velocity between the front and rear of the fan. Thus, the axial-flow fan blows air to the axial direction.
Therefore, the plurality of blades 11 can give lots of influences to the airflow efficiency and the generation of noise in the axial-flow fan 1. As shown in FIG. 5 showing the terms used to describe the blades 11 of the axial-flow fan 1 are defined, the axial-flow fan 1 should be designed optimally with a variety of blade designing factors, such as setting angle of the blades 11, camber ratio, cross-directional curvature, chord length and axial-directional inclination angle.
The camber ratio is obtained by dividing a maximum camber value into a chord length.
The setting angle is obtained by subtracting a stagger angle at which each blade 11 is erected from 90 degree.
Among the afore-described designing factors, herein, the setting angle and the camber ratio should be determined with great care.
As shown in FIGS. 5 and 6, the setting angle in the prior art is formed in such a way that it is constant from an intermediate region of each blade to a blade tip and decreases at a blade root, and the camber ratio decreases toward the blade tip from the hub 12. In this case, the percentage of decrease of the camber ratio is not over 30%.
According to the blade designing factors in the prior art, by the way, they exhibit the limits in suppressing the airflow noise generation during the rotation of the blades 11.